Television receiver blanking circuit



July 17, 1951. B. M. OLIVER TELEVISION RECEIVER BLANKINC CIRCUIT FiledJune 30, 1949 3 SheetIs-Sheetg /NVEN'OR By* B M; OLIVER I 4L/7g Ir. If/-ATTORNEY July 17, 1951 B. M. OLIVER 2,560,815

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I /NVEA/rof? E B M L/VER Julyl?, 1951 B. MQLNER 2,560,815

' TELEVISION RECEIVER BLNKING CIRCUIT Filed Jima so, '1949 ssheets-sheet s A TTORA/E V Patented `uly `17, 1951 elephoneLaboratoriesj. Incorporated,

- Application June 30,

Q laims This-.invention relates to television andymore vspecificallytothe blanking ofthe s canningbeam -of.a television receiver. .viewingtube.

It isA an object of this.invention..tocut..oi the beam current in atelevision. receiver .tubeduring vthe returntracefinterval morecompletely than it 4 has hitherto been. accomplisl'ied.

It is another obj ect of .this invention toperformthisbeamcut-oioperation Without any.- increase dri-expenditure oftransmitter power for the generation of blanking-pulses. It is a.further object .of-` this .invention td perform fthis. beam cut-offoperation without pro- Aviding additional circuits forgenerating a localblank-ing pulse .at .the television receiver.

--At `presenta complete television signal, such as thestandard R. M. A.Asignal,. ,for example, in-

cludes both horizontal and .vertical .--blanking pulses `Which-are used.at thereceiver .stationto -cut-o1 the' receivertube scanning beam duringboth horizontal and-.vertical return traces.. ATelevision viewing tubes.commonly have a beam cur- `rent versus gridvoltage characteristic.which has a remote fcut-off. When theltube. bias issetso .that .proper.contrast is obtained-,san.appreciable -beam..current flowsduring thenormal blanking period, when .the beam in-.the .tube shouldbe cut :of.AThis current. causesthereturn tracesonthe viewingltubescreentube-visible. Because of the increase-in transmitter. power that .wouldentail,

-..it.-does -not appear feasible tofincreasethe. amount of set up, thatinthe-.height of.=.the-.pedestal pulse upon Whichthe blanking pulseislocated, in .thevstandard picturesignal.to` ensure that 4the..-returnsweep line will be invisible. f

The .above and related objects. arel attained; in

- accordance with an exemplaryembodiment of the invention by providingas small tertiary transformer. winding on each of the cores, ofA:thevertical and horizontal .sweepoutputftransformers,

these tertiary windings being connectedinseries between ,the cathode of.thevieWing ,tube `and a pointof, xedpotential, .the seriescircuitalsoincluding a diode. During' the iiyback ofv either sweep Wave, a positivepulse/is appliedto theplate ,Ina modied form-.of the.invention,.separate.diodes areused,on .coupled to Aeach of the sweep. circuits.

`The invention Will-,bemore readi1y.understood .by referring. to.theollowing description takenin connection with theaccompanyingfdrawings .forming a part thereof, inwhich:

1949, `Serial No. 102,297

y2 f Fig. 1 is .a .block .schematic diagram .oi a. complete. televisionreceiver embodying a blanking -,circuit. in accordance. =with vtheinvention;

-;Fig. 2 isazcireuit.. diagram of a televisionre- 5 ceiver.: blankingcircuit .in. accordancel with. the

present .invention Eig. 3.is a.schematic circuit diagramillustrat- .inganother. form ofthis'invention; and Figs. .4f and 5 show.urtherimodicationsof the invention.

. .Whilethe invention-.is primarilyconcerned With a novel blanking.circuit in televisionreceivers, a brief deseriptionoa completatelevision. receiver .circuit .will .be given. to aid in.understandingrthe operation ofA thisinvention.

`..'..Referring..` more. .specieally to .the ....drawings, Fig. lshows,.by -way of. example. for .purposes of il- ..lustration,..a block.diagrarn of .acomplete tele- -\vision....'receiver.I system .l 0.-.;..'I.he. incoming .television. signalfrom thetransmitting station. isintercepted by the antenna l I, of any suitable form, .and applied. to.vthe radio frequency-.amplier i 2 v.wherel it is .amplified torthe`.desired level .and .conducted .to thefirst detector` E3.. .There it.is .demodulatedl ina manner. well Iknown,.down. tothe.desiredintermediate frequency of. the. system with -the^aid-oilthe-.oscillator i4. `Intermediate frequency signals are thenapplied bymeans-ofpaths A and B to the soundkandvpicture channels, respectively,of the reeciver. Thesound- `channel .includes anr am.pli1ier` l! 5,- in.ther input ycircuit of which is a tuned-circuit.-v -Thisrcombinationpasses ethesound-intermediate re'quency only Vand amy-pliiiesrit. Thesound signalstWhich-are frequencyA n1odulated), after being suitablyam-pliedinlamplier l5are applied to the discrimi- V naturO l 6'- Whichtransformslrthe frequency-modulated.. sound intermediate frequencysignals to "amplitude-modulated audio Afrequency signals. .The outputfofthe discriminatorl is then amplified by the audio amplifier Il andapplied to loudspeaker-I8. AThe signals in path B are Aapplied tothepicture intermediate frequency amplier 19,' which has ninitsinputcircuit*suitable-tuned circuits passing onlyv thev modulatedtelevision picture carrier. After;,suitable amplication by thevamplifier I9, the amplied signals are applied to the input of the seconddetectorj Where they are' demodulated down to video frequencies andapplied tothe .j videoamplifier2l.V -The outputof the video am- -plier-2l is applied to the modulating element 33 `of*the-viewing tube 30;thecustomary. direct-cur- .;rent restoring circuitfZZ being.also-connected. in this circuit..` .-'Ihe circuit. 22 reinserts Y, .the.directcurrent .level inthe .signal c omingfromfthe video 3 amplifier 2|before it is applied to the control grid 33 of the viewing tube 30.

The output of the video amplifier 2| is also applied to thesynchronizing separator 23 which strips off the video portion of thecomposite signal. The output of the synchronizing separator 23 containsthe vertical and horizontal synchronizing pulses only. A low-pass filteror integrating circuit in the output of the synchronizing separator 23allows only the vertical synchronizing pulses to pass through and affectthe vertical sweep circuit 24 while a differentiating circuit in theoutput of the synchronizing separator23 permits only horizontalsynchronizing pulses to be applied to and affect the horizontal sweepcircuit 25. Each sweep circuit applies a'saw-tooth current wave to thedeflecting coils. v

Connected to the vertical and horizontal sweep circuits 24 and 25,respectively, are the vertical and horizontal blanking circuits 26 and21. These blanking circuits make use of the large voltage pulses whichoccur during the return times of the sweep waves and the outputs ofthese circuits are positive pulses which are fed to the cathode 34 ofthe viewing tube 3B to cut off the beam during all return traces. Theamplitudes of these positive pulses are so controlled, in accordancewith this invention, that they completely cutoff the viewing tube beamduring all retrace periods.y YThe pulses occurring during the horizontalreturn traces are stepped up, rectified and filtered in the highvvoltage power supply 29, which furnishes the high voltage required forthe final anode 35 in the viewing tube 30. The low voltage power supply28 furnishes power to the various circuit components, to theaccelerating grid -36 in the viewing tube 30 and to the magneticfocusing coil 32 thereof. The beam in the tube 30 is formed andcontrolled in a well-known manner.

Reference will now be made to Fig. 2, which shows in circuit form thevertical and horizontal lblanking circuits 26 and 21 (shown in blocks inthe diagram of Fig. 1) together with their associated circuitconnections to other elements of the circuit of Fig. l. The verticalsweep circuit 24 terminates in the primary winding 40 of an outputtransformer Tl having a secondary winding 4I and a tertiary Winding 42,while the horiv zontal sweep circuit 25 terminates in a primary winding43 of an output transformer which has a secondary winding 44 and atertiary winding 45. In accordance with well known practice, the

4 pedance during this interval and practically the whole pulse isobtained across the resistor 41. The coupling and turns ratio of thetertiary windings 42 and 45 of the transformers 'II and T2,respectively, are so proportioned to the secondary windings 4| and 44thereof that the pulses obtained across the resistor 41 are suicient tocut off completely the beam currentin the viewing tube 30 during theretrace period which is at secondary windings 4| and 44 of these outputfor that reason merely by blocks 24 and 25), voltage pulses .appearacross the main secondary windings 4I .and 44, respectively. Thewindings 42 and 45 are so poled that corresponding positive pulses areinduced across their terminals and these positive pulses are applied tothe plate of the diode 46, resulting in this plate being momentarily ata higherpotential than the cathode. Thusthe diode presentsa low .seriesvirnthe end of every line scan in the case of the pulses produced inthewinding 43 and at the end of every field scan in the case of thoseproduced in the winding 40.

Alternativeforms of the invention are shown in Figs. 3, land 5.Y Inthese figures all elements whichare similar to corresponding elements inFig. 2 have been given the same reference characters.y K

The only difference `between the arrangement of Fig. 3 and'that of Fig.2 is that the `single diode 43 is replaced by a double diode 48 and thateach half of the diode 48 is connected in circuit with one of thewindings 42, 45. This arrangement may be slightly more preferable in thesitua- .tion where cross-talk and frequency response considerations areimportant since, in the arrangement of Fig. 3, the tertiary windings 42and 45.are independent of one another, that is, neither is loaded withthe strayrcapacity and series inductance of the other.

In the arrangement of Fig. 4, tertiary windings are not used. Instead,taps 50 and 5| are taken from the secondary windings 4| and 44,respectively, the lower terminal of each secondary being grounded. (Ifthe voltage required is high enough, the-taps 5|! and 5| vmay coincidewith the upper terminals of the respective secondaries.) A diode (52 or53) is connected in circuit with the lower half of a secondary winding,the 'twodiode circuits thus being in parallel.

In Fig. 5, the reactive pulses are induced directly from the sweep coils60 and 6| in coils 62 and 63 inductively coupled to the sweep coils. Ifdesired, one coil (62 or 63) can replace the two 'if the single coil isproperly oriented in the sweep yoke 3|. In this ligure a seriesarrangement (like that of Fig. 2) has been shown. The diode of Fig. 2has been replaced by a suitable crystal element 64 which, by way ofexample, can be germanium. Obviously, crystals can be used in the otherarrangements as well.

Obviously, if the video signal is applied to the cathode of thecathode-ray tube 30 (instead of to the control grid), the blankingsignals can be applied to the control grid 33. The tertiaries 42 and 45are then poled so as to give negative pulses during flyback and thediode 4B (or 48) is reversed so that the cathode is connected to thetertiaries and therplate is connected to the control grid and biasresistor.

Various other changes can be made in the embodiments described abovewithout departing Yfrom the spirit of invention.

What is claimed is:

l. Circuit means for blanking on its flyback strokes the beam producedin a cathode-ray tube by means including a beam control element,comprising means including a coil for producing sweep waves to deflect'saidv beam, means including a crystal limiter for obtaining a reactivepulse from said coil during each ilyback stroke of saidsweep waves, andmeans for applying said pulse to said control element in the propersense to cut off l :the beam.

2. Circuit means for blanking on its .ilyback strokes the beam producedin a cathode-ray tube by means including a beam control element,comprising means including a pair of coils for producing horizontal andvertical sweep waves to deflect said beams, a single coil inductivelycoupled to said pair of coils for obtaining a reactive pulse during eachiiyback stroke of said horizontal and vertical sweep waves, and meansfor applying said pulse to said control element in the proper sense tocut oi the beam.

3A -Circuit means for blanking on its ilyback strokes the beam producedin a cathode-ray tube by means including a beam control element,comprising means including a first pair of coils for producinghorizontal and Vertical sweep waves to deflect said beam, meansincluding a second pair of coils, the respective ones of the second pairbeing inductively coupled to the corresponding ones of the rst pair ofcoils, and an asymmetrically conducting device connected in circuittherewith for obtaining a reactive pulse during each flyback stroke ofsaid horizontal and vertical sweep waves, and means for applying saidpulse to said control element in the proper sense to cut o the beam.

4. `Circuit means for blanking on its ilyback strokes the beam producedin a cathode-ray tube by means including a beam control element,comprising means including a rst pair of coils for producing horizontaland vertical sweep waves to deect said beam, means including a secondpair of coils, the respective ones of the second pair being inductivelycoupled to the corresponding ones of the rst pair of coils, and anasymmetrically conducting device connected in a series clrcuit therewithfor obtaining a reactive pulse during each flyback stroke of saidhorizontal and vertical sweep waves, and means for applying said pulseto said control element in the proper sense to cut off the beam.

5. In combination, a television receiver picture tube having a beamcontrol element therein, a vertical sweep circuit for controlling thevertical deflection of the beam in said tube, a horizontal sweep circuitfor controlling the horizontal de REFERENCES CITED The followingreferences are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,153,655 Urtel et al Apr. 11,1939 2,235,053 Urtel Mar. 18, 1941 2,303,924 Faudell Dec. 1, 1942

